The present invention relates to variable stator blades of turbomachines, such as blowers, compressors, pumps and fans of the axial, semi-axial or radial type. The working medium (fluid) may be gaseous or liquid.
More particularly, this invention relates to at least one variable stator blade of a turbomachine or to a variable inlet guide vane assembly, if applicable. The respective blading is situated within a casing, which confines the passage of fluid through at least one rotor and one stator in the outward direction. While a rotor comprises several rotor blades attached to a rotating shaft and transfers energy to the working medium, a stator consists of several stator blades mostly fixed in the casing.
The aerodynamic roadability and the efficiency of turbomachines, for example blowers, compressors, pumps and fans, is limited in particular by the growth and the separation of boundary layers in the area of the radial gaps between the blading and the casing or the hub, respectively, these gaps being necessary at the annulus rim for reasons of design.
In particular on rotatable variable stators, the radial gaps generated by the required recesses before and after the trunnion are pronounced and entail considerable flow losses. In order to limit these losses, rotary bases of max possible size are usually used on the inward and outward ends of the variable stators to keep small the extension of the recesses in flow direction. Preferably, the rotary bases are provided such that they are situated in the crucial profile leading edge zones of the blade peripheral sections.
However, due to failure provisions and design constraints, configurations of variable stators quite frequently exist which have only small size and where the rotary bases are not situated far enough upstream. In this case, a considerable radial gap exists both before and after the rotary base. The state of the art does not provide any aerodynamically favorable solutions to this fundamental problem. The general concept of boundary influencing of radial running gaps by changing the type of skeleton line along the blade height is provided in the state of the art, however, the known solutions are not adequate and, therefore, not effective, in particular for the flow conditions at a blade end with rotary base and two partial radial gaps.
FIG. 1 schematically shows two blade configurations in the meridional plane defined by the radial direction r and the axial direction x, these blade configurations corresponding to the state of the art. The representation is limited to a variable stator borne in the hub and the casing, a bearing only in the casing or the hub, with full radial gap at the respective (other) blade end is however also possible in individual cases.
On the left-hand side, a conventional variable stator without variation of the type of skeleton line is shown. In this simplest standard case, the blade consists of only one block (Z0) in which the type of the skeleton line is specified according to fixed rules. This category includes the so-called CDA (controlled diffusion airfoils) according to U.S. Pat. No. 4,431,376. Aerodynamically, CDA aim at a moderate profile front load.
On the right-hand side, a conventional blade is shown whose rotating base extends up to the leading edge. In lieu of a completely uniform profile, the blade may also feature a continuous change of the profile type over the entire height according to the state of the art. Here, the entire blade is not represented by a block (Z0) of uniform profile, but by only one large transition zone. This includes concepts from known publications providing for a transition from a CDA type of skeleton line to a type of skeleton line that aims more at a profile back load in the blade outer areas (R. F. Behike, Journal of Turbomachinery, Vol. 8, July 1986).
In addition, attempts exist to positively influence the peripheral zone flow by specially shaping the blade stacking axis, for example by imparting a bend, sweep or dihedral to the blading (see EP0661413A1, EP1106835A2, EP1106836A2). None of the existing solutions refers to variable stators.